The present invention relates to methods for adding fertilizer nutrients to agricultural irrigation systems, including particularly agricultural micro-irrigation and sprinkler systems.
The agriculture industry has developed the practice of adding fertilizers to the plant environs, such as the soil, to enhance crop growth and subsequent yields. These fertilizers come in a variety of formulations depending on the specific crop to be grown and its nutrient requirements.
Fertilizers generally are classified according to their NPK content. NPK is common terminology used in the fertilizer industry and stands for: (1) N—the amount of nitrogen in the formulation as N; (2) P—the amount of phosphorus in the formulation as P2O5; and (3) K—the amount of potassium in the formulation as K2O. In other words, the N refers to nitrogen-containing compounds that are added to the soil and are utilized by the particular plant to satisfy its nitrogen requirement. The P refers to phosphorus-containing compounds that are added to the soil and are utilized by the particular plant to satisfy its phosphorus requirement (a nutrient required for plant growth). K refers to potassium-containing compounds that are added to the soil and are utilized by the particular plant to satisfy its potassium requirement (another nutrient essential for plant growth). Besides these basic nutrients or macronutrients, namely nitrogen, phosphorus and potassium, which are normally provided by the addition of fertilizers that typically are known as NPK fertilizers, other minor nutrients (micronutrients) can also be provided by the addition of fertilizers to the soil. Typical micronutrients are calcium, magnesium, sulfur, iron, zinc, manganese, copper, boron and molybdenum. The term “fertilizer” as used herein, unless expressly indicated otherwise, refers to NPK fertilizers, that is, fertilizers that include one of more of the macronutrients (nitrogen, phosphorus and potassium). An NPK fertilizer might, or might not, include or be combined (formulated) with materials that are added to the soil to provide micronutrient-containing compounds (micronutrient fertilizers).
As mentioned above, fertilizers contain macro and/or micro nutrients and it is these nutrients (“fertilizer nutrients”) that are taken up and utilized by the growing crops. A fertilizer, as that term is used herein and as generally understood, refers to the nutrient-containing materials that are physically employed to deliver fertilizer nutrients to a crop. The fertilizer-nutrient content of fertilizers can range from very low to very high. Conventional fertilizers typically (and low-nutrient-content fertilizers always) will contain non-nutrient materials that are extraneous to the crop's nutrient-uptake (“nutrient-extraneous materials”), but for practical and/or other reasons such non-nutrient materials may be necessary to the delivery of the nutrients. The process of delivering fertilizer nutrients to crops is referred to as fertilization although, as explained here, fertilizers typically contain nutrient-extraneous materials.
Growers added fertilizers centuries ago to grow better crops to feed increasing populations, typically by simple mechanical addition (mechanical delivery) to the soil in which the crop was grown. As populations increased further, irrigation of the land to improve crops and crop yields became another common agricultural practice. Fertilization methods ultimately were facilitated by the practice of adding fertilizers to the water being used to irrigate the crops. The term “fertigation” is used for this combination of irrigation and fertilization. Although extremely crude by today's standards, the early fertigation techniques provided higher crop yields and drastically reduced the labor expended in the addition of fertilizers.
Today's high demand for crops (food crops and otherwise) has turned agriculture into a technically-sophisticated business, and a business in which large corporate farms dominate the small family farm. The technical challenges faced by the modern agricultural industry include both the ever-increasing need for arable land, especially in the western and southwestern United States, and the decreasing availability and increasing cost of water. To conserve water, current conventional technology includes micro-irrigation systems that deliver precise amounts of water directly to the soil holding the root system of the plant that is being grown. In the past twenty to thirty years, a large percentage of crop producers in the western and southwestern United States have converted from flood and sprinkler irrigation systems to micro-irrigation technology. Micro-irrigation contains devices called emitters, micro-sprinklers or other such devices that provide the precise amounts of water directly to the desired soil site, namely the soil holding the roots of the plant or crop being irrigated. Similar to the advent of fertigation practices generally, upon conversion to micro-irrigation systems, modern farmers began adding fertilizers through them.
Micro-irrigation systems, unfortunately, are sensitive to water quality and the inclusion of fertilizers and other additives. The sensitivity of micro-irrigation systems to water quality and additives stems from the refinement of the micro components in a micro-irrigation system. These emitters, micro-sprinklers or other micro devices deliver the desired precise amounts of water so long as they do not plug or foul. Plugging occurs when deposits, from any source, build up inside these devices. The smallest particle or foreign material can cause fouling of these devices because these devices have very tiny orifices and/or a long tortuous narrow passageway that provide the requisite pressure for delivery of precise amounts of water in a uniform manner to each plant in the crop being irrigated. Water quality and the inclusion of fertilizers and other additives can, and frequently does, cause severe plugging problems. The problems arise from a number of factors: (1) the irrigation water is typically obtained from wells, reservoirs, canals, lakes, or rivers which contain various amounts of dissolved minerals; and (2) fertilizers, soil amendments and other additives can form insoluble salts and/or cause particulate formation when added to the water. Macro-irrigation systems mainly tolerate these conditions, while micro-irrigation systems are extremely intolerant.
In more detail, the addition of fertilizers or other materials, for instance soil amendments, to the micro-irrigation water increases the loading of inorganic salts over that already in the water. When the loading, or the combined loading, is too high, the solubilities of at least some of the naturally-occurring minerals and/or added compounds are exceeded and particulate formation increases dramatically. When particulates form, significant deposits begin to build up throughout the entire micro-irrigation system. The end result is plugging of the emitters or micro-sprinklers.
Plugging results in uneven distribution of water and nutrients to the crop being irrigated. In some cases, complete shut-down of the irrigation system occurs. Therefore problem-free use of additives such as fertilizers and/or soil amendments and the like in micro-irrigation systems is normally seen only in irrigation systems that use relatively pure water sources.
Various methods for the mechanical delivery of fertilizers to the crop are of course still available. Fertilizers can simply be spread onto the soil and mixed into the soil prior to planting the crop. Although this method of addition is still practiced today, especially in the case of inexpensive NPK sources, such as salt peter (potassium nitrate), phosphate rock (calcium phosphate) and gypsum (calcium sulfate hexahydrate, which is a source of the micronutrients calcium and sulfur), this spread-and-mix-in method is extremely expensive due to the high cost of the equipment employed, the fuel consumed and labor required.
Another mechanical method is to place or deposit fertilizers, such as solid fertilizers, alongside (by the side of) the plant rows in the field. This “side dressing” of additives is then plowed or tilled into the area surrounding the roots of the plant. This method is considered a “root zone” application of fertilizers because it provides a concentrated amount of fertilizer at or very close to the area at which absorption through the roots occurs, and it avoids fertilizing the areas between crop rows. Although this method reduces fertilizer usage (and thus fertilizer cost), the high equipment, fuel and labor costs remain.
Another mechanical delivery method of fertilizers is to spray concentrated aqueous solutions of fertilizers directed towards the root zone instead of depositing solid fertilizers in the side dressing method. Spraying eliminates the need to plow and mix the solid fertilizer into the soil, but does not significantly reduce overall costs because the spraying equipment is expensive and labor costs remain.
The fertigation process, in contrast, reduces the equipment, fuel and labor costs associated with the various methods for the mechanical delivery of fertilizers to the crop. In conventional fertigation practices, including micro-irrigation fertigation practices, commercial fertilizers are pumped directly into the irrigation system in single-shot or “slug” feedings and delivered to the root system or root zone together with the irrigation water that is already being supplied to the crop. In comparison to mechanical delivery/distribution methods, fertigation achieves a significant overall cost savings.
The conventional agricultural practice is to make intermittent or periodic applications of fertilizers. Such intermittent additions might be a single addition, or a plurality of additions, of large amounts (high concentrations) of fertilizer during a brief time interval each growing season or crop cycle. (The number of applications per growing season or crop cycle usually depends on the crop and/or the type of fertilizer being added.) When the fertilizer-delivery method is fertigation, fertilizers are typically slug fed into the irrigation system as quickly as possible to minimize the labor requirements and ease material handling. Slug feeding of a block (portion of a field) normally entails feeding the large amounts (high concentrations) of fertilizer to the irrigation water over a six to seven hour period during irrigation, and then, after the fertilizer feed is shut off, continuing the irrigation of that block for an additional two to three hours to rinse out all of the fertilizer that is contained inside the irrigation system, insuring that all of the fertilizer intended for the block is in fact delivered to the block.
The cost of commercial fertilizer formulations is, however, itself significant, and commercially viable fertilizer formulations (formulations sufficiently inexpensive for bulk agricultural use) typically include, as mentioned above, nutrient-extraneous materials which do not contribute to plant nutrition, and can even be undesirable components.
The term “micro-irrigation” as used herein and in the claims refers to microsprinkers, drip, and subsurface drip systems.